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文件名称：查询数据字典-SQL语言基础
文件大小：5.26MB
文件格式：PPT
更新时间：2021-04-25 19:38:28
SQL 基础
查询数据字典
*
查看用户所拥有的数据类型.
查看用户拥有的表、视图、同义词、序列.
SQL> SELECT *
2 FROM user_tables;
SQL> SELECT DISTINCT object_type
2 FROM user_objects;
SQL> SELECT *
2 FROM user_catalog;
描述用户拥有的表.
*
Querying the Data Dictionary
You can query the data dictionary tables to view various database objects owned by you. The data dictionary tables frequently used are these:
USER_TABLES
USER_OBJECTS
USER_CATALOG
Note: USER_CATALOG has a synonym called CAT. You can use this synonym instead of USER_CATALOG in SQL statements.
SQL> SELECT *
2 FROM CAT;
Instructor Note (for page 10-11)
Explain the things to consider when declaring a column as LONG datatype:
A LONG column is not copied when a table is created using a subquery.
A LONG column cannot be included in a GROUP BY or an ORDER BY clause.
Only one LONG column is allowed per table.
No constraints can be defined on a LONG column.